1. Field of the Invention
The present invention relates to non-asbestos friction materials which are well suited for use as brake pads, brake linings and clutch facings in automobiles and various kinds of industrial machinery.
2. Prior Art
A variety of inorganic fibers are used in automotive friction materials, and especially disk pads, to provide outstanding friction performance and noise characteristics. In particular, common use has been made of various types of whiskers, which are hard fibers that are effective for braking, and rock wool, which provides good strength. However, because inorganic fibers of this type which have a length of at least 5 μm, a diameter of up to 3 μm and an aspect ratio greater than 3 are known to be inhalable and potentially carcinogenic, efforts are being made to avoid their use. That is, the artificial inorganic fibers that have been used up until now are similar in shape to asbestos and are thought to be capable of triggering cancer in the same way as asbestos. Hence the interest in minimizing their use. Requirements for avoiding the use of similarly shaped fibers and materials which generate similarly shaped fibers as they break down are expected to become increasingly stringent.
Yet, fibers of this type have a low bulk density, which enhances the porosity of the friction material and in turn contributes to better fade performance and more effective braking action at high speeds. Failure to use such fibers lowers the porosity of the friction material and detracts from its fade performance and its effectiveness in high-speed braking.